Bolt size for oil pan drain plug?

Well this evening I attempted to do the first oil change(that I've done)on my 'stang that I've had about 5 months. Got my oil and filter and some Restore and got to work. The filter came off well enough, but the drain plug!
Let me tell you about this. First the plug looks like it is the stock plug, but it is not square, it is tapered(?)that is to say that the top of the hexagonal bolt is slightly less wide than at the bottom where the thick flange is(where it meets the pan). Is this normal, or is my pony the victim of a wanna-be mechanic? The biggest socket I have in metric is 15mm and no dice, I've got box-end wrenches in 16mm and up but nothing seemed to fit, so when the thing began to round off I just stopped, put on the new filter and enough oil to replace what the old filter had.
ANY SUGGESTIONS?? :shrug:

Also, since this poor car has a cast oil pan, can you not change the oil when the engine is hot? That is, has the hot pan expanded around the bolt(which I'm sure has expanded too) locking it in place? Reason I ask is I've NEVER had this happen on a stamped steel pan.
 
Yes, what I did was take out my old plug that leaked and looked as you described yours, then I placed some loctite on the threads and screwed it in to the oil pan. now I have no leak, and it comes with another threaded portion that screws onto it for a cap. Whe you change the oil you unscrew the cap and screw on thedrain valve with or without the attached hose, I dont use the hose. the mess is cut almost out completely unless you drop the filter on the floor. I do my oil hot now because nothing ever touches my hands. Like I said I have them on all of the family cars. Brass Fittings not prone to rust.
 
Ya that sounds like a good idea, I'm sick of trying to find the time to get my oil changed by someone else but if I can simplify it a whole lot then I can just do it myself instead of driving down to Canadian Tire and waiting in line for a grease monkey to do it for me :D
 
Get the Shurflo pump, it kicks butt!!!!!!!
I got it today and did my oil change with it earlier this evening, wow what a difference! I shoulda got one for my Dad on Father's Day.
NO dropping the drain plug into 100+F. oil
NO extended time beneath the car(boy is a 'stang low to the ground, this is my first pony car)
NO fighting with a drain plug put on by a guy who is worried about losing his job because last week the company had to buy an engine because Lubrication Tech "Bob" forgot to snug up the drain plug on that Lebaron...
NO mess, oil is pumped directly into container, no pouring out of the oil change pan
CERTAINLY THE BEST $15 I'VE SPENT THIS YEAR!!!!!!! :nice: